Processes such as ink jet printing and lithography are used to fabricate a wide range of electronics and bio-sensors at the micro- and nano-scale (μ/n-scale). Despite advancements in these processes over time, they are not always able to meet certain performance requirements (e.g. resolution, material diversity, or process flexibility) and/or cost requirements (e.g. material use or cycle time), particularly in emerging applications in biotechnology and flexible electronics.
Ink jet printing has seen rapid development in the past few decades. Some ink jet systems are able to provide high throughput (e.g., 50-175 kHz jetting frequency) at low system costs. Printing processes are generally considered to be environmentally friendly processes as applied to device fabrication since they are additive processes that produce minimal waste. But the nozzle diameter of a typical ink jet print head, such as a thermally actuated bubble jet system print head, is about 20-30 μm, resulting in a print resolution that is too coarse for micro-scale applications. Some ink jet print systems use piezoelectric materials to generate mechanical waves that eject ink droplets from the nozzle. But the mechanical vibration of the nozzle can limit the accuracy of such systems, rendering them unable to meet the tight resolution requirements of μ/n-scale applications. The types of ink materials that can be used in thermal- and piezoelectric-actuated ink jet systems is also somewhat limited by nozzle clogging issues and the need to withstand exposure to the temperatures used in thermal actuation.
Lithography processes have proven capable in mass manufacturing and in some μ/n-scale manufacturing applications, but are not able to provide the flexibility, material diversity, and cost effectiveness required for all μ/n-scale manufacturing applications, particularly in new and emerging applications. Optical lithography employs an etching process to produce a specific pattern determined by a pre-designed mask. While highly accurate, this process is not suitable for biological materials or electro-optical components that are susceptible to the aggressive materials used in the etching process. The masking requirement also makes photolithography less flexible than printing processes, not to mention more time consuming and costly. Nanoimprint lithography can achieve high resolution and accuracy, demonstrates high throughput at a low cost for mass production, is compatible with many materials, and can create 3D structures at the nano-scale. However, nanolithography also requires a mask and is thus less flexible than printing processes. Lithography processes can also be relatively complex, often including multiple steps for fabrication, and is generally not considered environmental friendly, as etching away material necessarily includes material waste.
Electrohydrodynamic jet printing, also known as e-jet or EHD printing, is a type of printing that has shown promise for use in printed electronics and bio-sensor applications. A typical e-jet printing process relies on an electrostatic field between a conductive nozzle and a conductive substrate to extract a printing fluid from the nozzle without the increased temperatures or mechanical vibrations associated with thermal- and piezoelectric-actuated ink jet printing. E-jet printing has been somewhat limited by low product throughput and the requirement for a conductive substrate to generate the necessary electrostatic field. Process sensitivity has also plagued e-jet printing. For example, nozzle-to-substrate distance can be a critical parameter affecting the generated ink-extraction field, thus generally limiting the process to flat substrates. Additionally, once a layer of non-conductive ink is deposited onto the conductive substrate, the character of the generated electrostatic field is changed, greatly limiting the use of e-jet printing in 3D-printing applications.